The lipid content of human sweat was determined in thermally induced sweat collected over a Vaseline or silicone barrier placed on the skin (clean sweat) and in sweat scraped from the skin surface without a barrier coating (scraped sweat). Lipids were extracted from concentrated sweat samples into chloroform:methanol and estimated by thin-layer chromatography in conjunction with photodensitometry. Scraped sweat contained 4 to 10 times more lipid than clean sweat and included cholesterol sulphate and ceramides resembling those found in the stratum corneum. In contrast, clean sweat contained only small amounts of free fatty acids and sterol. A marked individual and daily variation in sweat lipid content was also noted. The study indicates the importance of avoiding epidermal contamination when collecting sweat and the usefulness of our sweat collection method.